Because it doesn't require it... there was no such feature in ANY click fest hack and slash game....

LoL - So you are telling me that my bad arse level 20 killer, Master of Pain, Holy Terror of with glowing eyes and flames coming out of him can be stopped dead in his tracks by a row of flowers barely a few inches off the ground. I think the truth here is that they are using the no-jump feature as a invisible wall to limit your movement. This IMHO limits the feeling of freedom to move in a 3d world especially in a game like this.